Упражнения

Упр. 1. Найдите в тексте английские эквиваленты следующих слов и словосочетаний:

1. Устранить\ исправлять дефекты; 2. ремонтная сварка; 3. после воздушно-дуговой строжки производится шлифовка; 4. с помощью тех же методов контроля, что и первоначально; 5. с помощью локализованного тепла; 6. планы осмотра и испытаний; 7. к полному удовлетворению компании; 8. высокая степень несоответствия при выполнении работ; 9.но не ограничиваться; 10.повторная аттестация персонала; 11. эксплуатация в неблагоприятных погодных условиях; 12. рассчитанный на долгий срок службы.

Упр.2 . Переведите следующие слова и словосочетания:

1. To verify removal of defects; 2. member distorted by welding; 3. by mechanical means; 4. possible degradation of the material properties; 5. project requirements; 6. due consideration; 7. remedial action;; 8. to call for special consideration; 9. criticality of the design; 10. fabrication tolerances; 11. increased inspection.

Unit 30. FUNDAMENTALS OF THE RESISTANCE METHOD

Two distinct forms of electric apparatus are in use, one producing heat by the resistance of the metal being treated to the passage of electric current, the other using the heat of the electric arc.

The resistance process is of the greatest use in manufacturing lines where there is a large quantity of one kind of work to do, many thousand pieces of one kind, for instance. The arc method may be applied in practically any case where any other form of weld may be made. The resistance process will be described first.

It is a well known fact that a poor conductor of electricity will offer so much resistance to the flow of electricity that it will heat. Copper is a good conductor, and a bar of iron, a comparatively poor conductor, when placed between heavy copper conductors of a welder, becomes heated in attempting to carry the large volume of current. The degree of heat depends on the amount of current and the resistance of the conductor. In an electric circuit the ends of two pieces of metal brought together form the point of greatest resistance in it, and the abutting ends instantly begin to heat. The hotter this metal becomes, the greater the resistance to the flow of current; consequently, as the edges of the abutting ends heat, the current is forced into the adjacent cooler parts, until there is a uniform heat throughout the entire mass. The heat is first developed in the interior of the metal so that it is welded there as perfectly as at the surface.

The electric welder is built to hold the parts to be joined between two heavy copper dies or contacts. A current of three to five volts, but of very great volume (amperage), is allowed to pass across these dies, and in going through the metal to be welded, heats the edges to a welding temperature. It may be explained that the voltage of an electric current measures the pressure or force with which it is being sent through circuit and has nothing to do with the quantity or volume passing. Amperes measure the rate at which the current is passing through the circuit and consequently give a measure of the quantity which passes in any given time. Volts correspond to water pressure measured by pounds to the square inch; amperes represent the flow in gallons per minute. The low voltage used avoids all danger to the operator, this pressure not being sufficient to be felt even with the hand resting on the copper contacts.

Current is supplied to the welding machine at a higher voltage and lower amperage than is usually used between the dies, the low voltage and high amperage being produced by a transformer incorporated in the machine itself. By means of windings of suitable size wire, the outside current may be received at voltages ranging from 110 to 550 and converted to the low pressure needed.

The source of current for the resistance welder must be alternating, i.e. the current must first be negative in value and then positive, passing from one extreme to the other at rates varying from 25 to 133 times a second. This form is known as alternating current, as opposed to direct current, in which there is no changing of positive and negative.

The current must also be what is known as single phase, i.e. a current which rises from zero in value to the highest point as a positive current and then recedes to zero before going to the lowest point of negative value. Two-phase or three-phase currents would give 2 or 3 positive impulses during this time. As long as the current is single phase alternating, the voltage and cycles (number of alternations per second) may be anything convenient. Various voltages and cycles are taken care of by specifying all three points when designing the transformer which is to handle the current.

Direct current is not used because there is no way of reducing the voltage conveniently without placing resistance wires in the circuit and this uses power without producing useful work. Direct current may be changed to alternating by having a direct current motor running an alternating current dynamo, or the change may be made by a rotary converter, although this last method is not so satisfactory as the first.

The voltage used in welding being so low to start with, it is absolutely necessary that it be maintained at the correct point. If the source of current supply is not of ample capacity for the welder being used, it will be very hard to avoid a fall of voltage when the current is forced to pass through the high resistance of the weld. The current voltage for various work is calculated accurately, and the efficiency of the outfit depends to a great extent on the voltage being constant. In order to hold the voltage constant, the Toledo Electric Welder Company has devised connections which include a rheostat to insert a variable resistance in the field windings of the dynamo so that the voltage may be increased by cutting this resistance out at the proper time. An auxiliary switch is connected to the welder switch so that both switches act together. When the welder switch is closed in making a weld, that portion of the rheostat resistance between two arms determining the voltage is short-circuited. This lowers the resistance and the field magnets of the dynamo are made stronger so that additional voltage is provided to care for the resistance in the metal being welded.

In a typical machine on top of the welder there are two jaws for holding the ends of the pieces to be welded. The lower part of the jaws is rigid, while the top is brought down on top of the work, acting as a clamp. These jaws carry the copper dies through which the current enters the work being handled. After the work is clamped between the jaws, the upper set is forced closer to the lower set by a long compression layer. The current being turned on with the surfaces of the work in contact, they immediately heat to the welding point when added pressure on the lever forces them together and completes the weld.

The transformer is carried in the base of the machine and on the left-hand side is a regulator for controlling the voltage for various kinds of work. The clamps are applied by treadles convenient to the foot of the operator. A treadle instantly releases both jaws upon the completion of the weld. One or both of the copper dies may be cooled by a stream of water circulating through it from the city water mains. The regulator and switch give the operator control of the heat, anything from a dull red to the melting point being easily obtained by movement of the lever.

VOCABULARY

Manufacturing line – производственная линия, конвейер

Flow of current – ток

Electric circuit – электрическая цепь

Abutting ends – торцевые, смежные концы

Die \ contact – контакт, контактная колодка

Electric welder – сварочный аппарат, агрегат

Winding – виток (обмотки)

Single phase - однофазный

Direct current motor – двигатель постоянного тока

Alternating current dynamo – генератор переменного тока

Connection – зд. схема подключения

Field winding – обмотка возбуждения

Upset - осадка

Setting – режим (сварки)

Cycles – зд. частота

Rotary converter – одноякорный \ вращающийся преобразователь

Ample capacity – полная емкость

Outfit – оборудование, установка

Gauge – зд. профиль

Upset - осадка

Setting - режим

Rheostat - реостат

To cut resistance out – отключить сопротивление

Auxiliary switch – вспомогательный переключатель

Arm – консоль сварочного аппарата

To short-circuit – замкнуть накоротко

(Сompression) lever – рычаг (механический)

Treadle – педаль